linux-kernel - Re: [PATCH v2] arm64: jump_label: use constraints "Si" instead of "i"

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Date: Tue, 20 Feb 2024 12:05:30 +0000
From: Will Deacon <will@...nel.org>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>,
	Arnd Bergmann <arnd@...db.de>, Fangrui Song <maskray@...gle.com>,
	Catalin Marinas <catalin.marinas@....com>,
	linux-arm-kernel@...ts.infradead.org,
	Jisheng Zhang <jszhang@...nel.org>,
	Dave Martin <Dave.Martin@....com>,
	Peter Smith <peter.smith@....com>, llvm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] arm64: jump_label: use constraints "Si" instead of "i"

On Mon, Feb 19, 2024 at 04:41:03PM +0100, Ard Biesheuvel wrote:
> On Mon, 19 Feb 2024 at 15:43, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > > > > > Changes from
> > > > > > arm64: jump_label: use constraint "S" instead of "i" (https://lore.kernel.org/all/20240131065322.1126831-1-maskray@google.com/)
> > > > > >
> > > > > > * Use "Si" as Ard suggested to support Clang<19
> > > > > > * Make branch a separate operand
> > > > > >
> > > > > > Changes from v1:
> > > > > >
> > > > > > * Use asmSymbolicName for readability
> > > > >
> > > > > But it still fails on gcc-5:
> > > > >
> > > > >     arch/arm64/include/asm/jump_label.h:25:2: error: invalid 'asm':
> > > > > invalid operand
> > > > >       asm goto(
> > > > >       ^
> > > > >
> > > > > http://kisskb.ellerman.id.au/kisskb/buildresult/15129281/
> > > > >
> > > >
> > > > How odd. godbolt.org has 5.4 and it seems perfectly happy with it.
> >
> > > https://godbolt.org/z/GTnf3vPaT
> >
> > I could reproduce the issue on v6.8-rc5 using arm64 defconfig
> > and x86_64-gcc-5.5.0-nolibc-aarch64-linux.tar.xz from
> > https://cdn.kernel.org/pub/tools/crosstool/files/bin/x86_64/5.5.0/:
> >
> 
> OK, I managed to do so as well.
> 
> And GCC 6.4 from the same source works correctly.
> 
> Not sure whether there are any plans to bump the minimal GCC version
> any time soon (cc'ing Arnd), but we should probably drop this change
> until that happens.

Yup, makes sense to me. I'll revert the original change and we can bring it
back later if we decide to bump the minimum GCC version.

Cheers,

Will